I. Field of the Invention
This invention relates generally to non-contaminating pressure transducer modules, and more particularly relates to a pressure transducer module that effectively operates within Ultra High Purity (UHP) processing equipment that utilize UHP chemicals and require UHP conditions. The pressure transducer module of the present invention provides a continuous measurement of the pressure within a fluid flow circuit of the UHP processing equipment without contaminating the fluid within the circuit. An isolation member which isolates a pressure sensor from the chemically corrosive fluid flow. The pressure sensor adjoins the isolation member without compromising the accuracy of the pressure measurement or increasing the risk of fluid contamination. The isolation member may be interchangeable and eliminates the need to submerge the pressure sensor in an oil or other fluid, thereby eliminating potential contaminants to the fluid flow channel.
II. Discussion of the Related Art
Over the years, the processing equipment used during the manufacture of semiconductor substrates has evolved, attempting to isolate the substrate from the presence of any small particles, metallic ions, vapors or static discharge in the environment during the manufacturing process. The processing equipment may be used to manufacture, for example, a wafer, LCD, flat panel display, and/or memory disks. Significantly, industry standards require ultra high purity environments within the processing equipment.
During the processing of semiconductor substrates, the substrate is commonly subjected to chemically corrosive fluids and high temperatures. These fluids are delivered and removed from the substrate by the UHP processing equipment through fluid lines. The various components of the processing equipment are commonly designed to reduce the amount of particulate generated and to isolate the processing chemicals from contaminating influences. Typically, the processing equipment will include monitoring and sensing devices connected in a closed loop feedback which are used in monitoring and controlling the equipment. These monitoring and sensing devices must also be designed to eliminate any contamination which might be introduced and must operate with accuracy through a wide range of temperatures.
A highly corrosive environment may be created when aggressive processing chemicals are delivered to the processing equipment. Liquid transporting systems carry these chemicals from supply tanks through pumping and regulating stations and through the processing equipment itself The liquid chemical transport systems, which includes pipes, tubing, valves, and fittings, are frequently made of plastics resistant to the deteriorating effects of the aggressive processing chemicals. Of course, anything mechanical is subject to potential leakage and such leakage can create extremely hazardous conditions both to the processing of semiconductor wafers or other products and also to personnel who may have to tend and maintain the processing equipment. Hence, the chemical transport system must be designed to detect and avoid such leakage.
Monitoring and sensing devices are incorporated into the UHP processing equipment to detect, for example, this leakage. The monitoring and sensing devices may incorporate sensors which also must be designed to avoid the introduction of particulate, unwanted ions, or vapors into the processing steps. Monitoring the pressure within the chemical transport system is useful for several reasons. First, a change in pressure within the system may indicate leakage within the system. Second, the pressure within the transport system is regulated to avoid exceeding predetermined safety limits. Third, the pressure within a fluid flow circuit may be controlled to actuate various processing tools connected to the processing equipment.
When highly corrosive hazardous chemicals are used, such corrosive atmospheric environments are extremely hard on the monitoring and sensing equipment. Further, the monitoring and sensing equipment may transmit wafer damaging particulate, ions, or vapors as a result of exposure to the corrosive atmospheric environment. Metals, which are conventionally used in such monitoring devices, cannot reliably stand up to the corrosive environment for long periods of time. Hence, the monitoring and sensing devices must incorporate substitute materials. Significantly, a mere substitution of materials in the monitoring device oftentimes produces a device with other deficiencies, including leaks and inoperativeness. Although pressure sensors have generally been developed for use in other applications, these sensors are not particularly well suited for use in semiconductor substrate UHP processing equipment. Exemplary of such a fluid pressure sensor are the pressure gauges disclosed by Schnell in U.S. Pat. No. 4,192,192 and Zavoda in U.S. Pat. No. 3,645,139. The sensing portion of the pressure gauge of the '192 and '139 devices are contained within a housing that requires a cavity filled with a sensor fluid or oil. The cavity is formed adjacent the fluid flow and separated by a protective member. The protective member is described by Schnell '192 as being made from a metal having a TEFLON.RTM. coating being applied thereto. TEFLON.RTM. coatings are permeable and allow small amounts of fluid to permeate through the coating. When subjected to chemically corrosive fluids used in semiconductor substrate processing equipment, the processing fluids permeate through the coating of the protective member, corrode the metal and permeate back through the coating thereby contaminating the processing fluids. This contamination is not acceptable in UHP processing equipment. Further, it is believed that the stiffness of the metal coated '192 protective member decreases the accuracy and resolution of the measured pressure. Hence, use of the sensors disclosed in the '192 and '139 patents are not acceptable in the UHP processing equipment.
The protective member of the Zavoda '139 device is described as a TEFLON.RTM. molded single-unitary structure having a wavelike cross-section to enhance the flexibility and displacement characteristics of the diaphragm. TEFLON.RTM. films and molded parts are also permeable and allow small amounts of fluid to permeate through the part. Thus, when positioned in-line within the fluid flow circuit of semiconductor substrate processing equipment, the sensor fluid or oil contained within the housing of Zavoda would permeate through the protective member and contaminate the fluid within the fluid flow circuit. Also, a diaphragm having a wavelike cross-section as described by Zavoda '139 is believed to decrease the accuracy of pressure measurements when measured over a wide range of temperatures. Significantly, Zavoda does not describe a diaphragm that adjoins an enclosed sensor. Further, it is believed that adjoining the sensor to the diaphragm disclosed by Zavoda would result in an inoperable or unreliable pressure sensor having minimal accuracy and resolution. Hence, there is a need for a chemically inert pressure sensor module that isolates the sensor from the fluid flow without affecting the accuracy of the pressure measurements or requiring sensor fluid.
A device in accordance with the teachings of either the '192 or '139 patent includes additional shortcomings when used in semiconductor substrate processing equipment. The fluid contained within a cavity of the pressure gauge of these devices is typically a silicone oil. A change in pressure within the fluid flow of the processing equipment affects the oil pressure within the cavity of these devices. Also, the oil within the cavity typically has large thermal expansions which cause large deflection changes in the protective member. The large deflection changes in the protective member increases the likelihood that the oil within the cavity will leak into the fluid flow, contaminating the flow circuit of the processing equipment. Also, the accuracy of the pressure gauge is negatively affected by the large thermal expansions of the oil. Hence, a need exists for an in-line pressure gauge that does not leak contaminating fluids into or out of the fluid flow circuit. Also, a need exists for an in-line pressure sensor, wherein the accuracy is not affected by thermo changes within the fluid flow circuit.
Other devices have been described for measuring a pressure within a fluid flow circuit. For example, Ridenour in U.S. Pat. No. 5,063,784 and Sorrell in U.S. Pat. No. 5,183,078 describe devices that may be connected in-line within a fluid flow circuit to measure the pressure therein. Each device includes a check valve which functions as a barrier between the fluid flow circuit and a remote pressure sensor. When the valve is opened, fluid from the circuit flows through the valve and a certain amount of contaminating back flow results. Thus, the devices disclosed by Sorrell and Zavoda are not suitable for use in environments where high purity is desired.
Collins et al., in U.S. Pat. No. 5,316,035 (the '035 patent) describes a device that appears suitable for use in highly corrosive environments where high purity is desired. Collins describes a capacitance proximity monitoring device that detects the presence of liquids in the environment. The capacitance proximity device determines the change of electrical characteristics within a predetermined area as various fluids flow past the predetermined area. The changes in current from the sensing field is utilized to detect the presence of liquids within the sensing field. Although utilizable in high purity environments, the '035 patent does not describe a device capable of measuring pressure within a fluid flow conduit of the processing equipment.
Therefore, a need exists for a non-contaminating pressure transducer which may be positioned within a fluid flow circuit carrying corrosive materials, wherein the pressure transducer determines either a gauge pressure or absolute pressure of the fluid flow circuit with a reliable resolution and accuracy. A need also exists for a pressure transducer that avoids the introduction of particulate, unwanted ions, or vapors into the flow circuit. The present invention overcomes these and other disadvantages of the related art.